The present invention relates to processing the power obtained from a RF power sensor used in association with digital and analog radio telephones to become a detector voltage in direct linear proportion to the entire power range used.
In radio telephone systems, at both fixed and mobile stations, information regarding the station's power must be obtained in order to control this power. The power control range in radio telephones is wide, and numerous power levels are provided. The power levels must be very stable regardless of temperature. Reaching and maintaining stability is difficult, particularly at extreme temperatures; therefore, the requirements set for the power control of the means are great. Power control is particularly difficult when the power level is low because when the power is on the order of the milliwatt magnitude, the voltages obtained from the sensor of the power level detector are very low. The situation becomes even more difficult if the steps of the power levels are small. For instance, the power range in the GSM system is organized into only 2 dB steps, and this emphasizes the effect of the exponential ratio of power and voltage. Thus, the difference between the DC voltages of adjacent small power levels obtained from the power sensor remains marginal. Hence, the power control resolution is required to be extremely wide, which emphasizes the effect of interferences and ambient factors. The instability of low power levels increases costs for radio telephone production, and there is a risk that, owing to the effect of aging and other factors, the radio telephone's ability to meet the requirements set for its power stability will deteriorate over time.
It is known in the art to employ a circuit implementing detector diodes as a power level detector. The voltage obtained from this kind of detector is exponentially proportional to the power (dB) to be indicated, due to, for instance, the specific graph (characteristics) of the diode. As a result, at low power levels small power variations cause a hardly observable change in the voltage of the detector so that the above-mentioned problems still exist.